Plastic and paper pollution are reaching epidemic levels, polluting our oceans and quickly filling our available landfill capacities. Conventional disposable food service items are an example of this pollution. They are commonly made from paper or paperboard which is coated, impregnated, or laminated with a polymeric waterproofing material such as wax polyethylene or a polyester film or made from one of a variety of plastics (polystyrene is the most common). These materials have good to excellent resistance to moisture, can be insulating (e.g., foamed polystyrene or “Styrofoam”), and are inexpensive and durable. In addition, ovenable disposables are made from aluminum or CPET, commonly known as dual ovenable plastic.
The current drive by many countries to reach industrial status has greatly reduced the free time that its working population has for preparing food at home or for creating specialty items. As this trend continues to accelerate, the demand for disposable packaging is growing exponentially. Moreover, there is a growing recognition that the environmental costs (from production through disposal) of using these “cheap” materials may be quite high compared to natural products that are biodegradable and/or compostable. The expected lifetime of a polystyrene cup, for example, can be up to 500 years, and each American disposes an average of about 100 of these cups per year. Further, polystyrene is made by chemical processing of benzene and ethylene, both byproducts of a petroleum industry that is recognized for its environmental problems. While governments around the world have all but given up on implementing recycling programs as unworkable and too costly, they still have the problem of garbage accumulation to solve and many have started taxing non-degradable packaging. There is a need to address environmental concerns with respect to disposable food service and food packaging items.
The biggest challenge in making durable, disposable food service and packaging articles that address the environmental concerns discussed above is an inherent lack of moisture resistance. All biological processes that result in the degradation of organic materials rely upon water to function. As a result, it is very difficult to make a material highly moisture resistant that will also be biodegradable and compostable.
One method currently used to address environmental concerns about conventional disposable food container products is the manufacture of starch and/or cellulosic-based disposable food service items such as trays, plates, and bowls. Many starch and/or cellulosic-based packaging materials have several drawbacks, the most important being that the containers are susceptible to water. Cooked, unmodified starch is typically water soluble. Because all of the starch-based biodegradable food service items currently being manufactured are formed in heated molds, much or all of the starch in these items is cooked, and the products thus formed are sensitive to moisture. Cellulose fiber (e.g., paper and paperboard or pulp) and cellulose derivatives (e.g., cellophane and cellulose esters, ethers, etc.) are also quite permeable to water. When exposed to water, other aqueous fluids, or significant amounts of water vapor, these items may become very soft, losing form-stability and becoming susceptible to puncture by cutlery (e.g., knives and forks).
Improvements to and/or cellulosic-based biodegradable articles may be made to make them more moisture resistant. Improvements may also serve to strengthen the matrix material by enhancing the chemical and physical properties, and include the addition of wax or wax emulsions, fiber sizing agents, plasticizers, polymers, or a combination thereof. These articles perform the best under low-moisture conditions in food and non-food applications alike. Examples of said biodegradable containers are found in U.S. Pat. No. 7,553,363, granted Jun. 30, 2009; U.S. patent application Ser. No. 11/285,508, filed Nov. 21, 2005; U.S. patent application Ser. No. 12/168,049, filed Jul. 3, 2008; and U.S. patent application Ser. No. 12/257,289, filed Oct. 23, 2008; which, by reference, are incorporated herein in their entirety.
Some applications further require increased moisture resistance. For example, some convenience foods and drinks that require the addition of hot or boiling water such as soups or instant coffee must have a container that is more capable of resisting moisture absorption than a plate that is being used to heat solid food, such as a piece of leftover chicken. Further examples of the type of demanding applications that may require increased moisture resistance are pre-made, ready to eat meals for schools, prisons and other institutions, bakery items, frozen or refrigerated prepared meals, soup and noodle bowls, cups for coffee, hot chocolate, and other beverages, cereal bowls, ice cream and yogurt cups, and other similar high-moisture applications. One way to improve to the moisture resistance of various biodegradable materials is by applying a coating to the product. In addition to moisture resistance, some applications require non-stick or release characteristics. Such applications include bakery items, for example, pies, breads, muffins, pizza, cakes and the like.
In keeping with the desire to produce biodegradable and compostable containers, it is also desirable for a coating that increases the moisture resistance to be biodegradable and compostable. Cellulose esters are biodegradable and are known in the art as base polymers used in coatings and inks. By themselves, cellulose esters have a very high moisture vapor transmission rate (MVTR) and thus offer only short term resistance to water.
A coating that has moisture resistance sufficient for high-moisture applications as described above, as well as economically efficient and completely biodegradable and compostable has yet to be perfected.
It is therefore an object of some embodiments of the present invention to provide a fully biodegradable and compostable coating with improved moisture resistance such that the Moisture Vapor Transmission Rate (MVTR) is significantly reduced, thus allowing use in high moisture applications.
It is further an object of some embodiments of the present invention comprising wax to reduce or eliminate the need to coat food service or packaging items at elevated temperatures or to expose such items to prolonged drying/heating above the melting point of the wax in order to obtain the lowest MVTR.
It is a further object of some embodiments of the present invention to provide a highly moisture-resistant coating that is also cost-effective.
It is a further an object of some embodiments of the present invention to provide a highly moisture-resistant coating that is dual ovenable, heat sealable, and which provides product release in bakery applications.